Method of mineral raw materials processing

ABSTRACT

The invention relates to methods of precious metals recovery from raw materials containing chlorides of earth metals, for example slimes. This method comprises the steps of cinder processing carried out in two steps. At the first step, a secondary enrichment by water washing is carried out with a ratio (S:L) ranging from 1:0.7 to 1:2.5. Then, at the second step, the washed cinder is leached by hydrochloric acid with a ratio (S:L) ranging from 1:2 to 1:3.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase application of a PCT application PCT/RU2009/000458 filed on 8 Sep. 2009, published as WO2010/036144, whose disclosure is incorporated herein in its entirety by reference, which PCT application claims priority of a Russian Federation patent application RU2008/138738 filed on 29 Sep. 2008.

FIELD OF THE INVENTION

The invention relates to methods of mineral raw materials processing and may be applied to the recovery of precious metals (platinum, palladium, gold, etc.) from various types of mineral raw materials containing chlorides of alkali and earth metals, like slimes of potassium production.

A known method of mineral raw materials processing described in a reference book “Technological evaluation of mineral raw materials” (edited by doctor of engineering sciences P. E. Ostapenko, Moscow, publisher “Nedra”, 1990, p.98) includes a process of ores enrichment by disintegration (loosening, dispersion) of a clay material which is part of ores.

The enrichment may be executed either by solely using water, or by using water in conjunction with mechanical action of appropriate apparatus, or by using water and compressed air with the subsequent removal of a dispersed portion in the form of slimes. The slimes contain clay dispersed in water and small ore particles. After the slimes removal the resulted washed product is a granular (loose) material including the ore mineral grains and non-ore mineral grains. ‘Washing’ herein means a process of ores enrichment and the washing is applied to manganese ores, brown iron ores, chromium ores, etc.

A disadvantage of the above-mentioned method is the impossibility of recovery of palladium and silver.

Another method of potassium production slimes processing (Russian Federation Patent # RU2132398, published on Jun. 27, 1999) is known.

According to the method taught in RU2132398 RF, gold-containing slimes are cleaned of salts with the help of water, after which the salted water, formed during cleaning, is removed; then fresh water is added to the slimes, and then the produced pulp is chlorinated by chlorine gas while care is taken to ensure that the active chlorine content in the leaching solution is maintained within 0.3-2.0 gram/L. After the leaching process is completed, gold is recovered by a sorption process.

The disadvantages of the foregoing method include the need to thoroughly clean the chlorides and use elemental chlorine, a high toxic substance, for gold recovery, and the impossibility of recovery of palladium and silver.

From the technical viewpoint, the closest to this invention is a method of precious metals recovery from mineral raw materials (Russian Federation Patent # RU2291907, MPK7 S228 11/00, published on January, 2006). According to the method described in RU2291907, the mineral raw materials are cleaned from excess chlorides with the help of water until the chlorides content is within 7-13%, after which the cleaned pulp undergoes concentration and then the concentrated product is dried and roasted at the temperature of 600-700° C. The precious metals are leached from the cinder using a diluted solution of aqua-regia and then recovered from the produced pulp by means of sorption.

A disadvantage of this method is the following: the exclusion (in order to avoid a loss of palladium with washing solutions due to a considerable solubility of palladium compounds) of the washing-off operation to remove chlorides leads to the necessity of processing the mineral row materials with a high content of chlorides of alkali and earth metals, which must be dissolved for precious metals recovery.

As a result, for the cider leaching it is necessary to use a high solid-to-liquid (S:L) ratio in order to avoid the chloride crystallization during the cooling of the solutions, and therefore the amount of equipment necessary for the leaching processes and subsequent sorption of metals from the pulp increases considerably.

The aforesaid disadvantage is eliminated by means of using the proposed method.

The technical result achieved according to the proposed method consists in decreasing the volume of pulps produced during the leaching, and therefore reducing the amount of hydraulic-metallurgical equipment for the pulps' processing, and also in increasing the percentage of recovered precious metals, and returning a considerable part of potassium chloride to the production process, which part otherwise would be lost with the slimes.

To achieve the aforesaid technical result, in the inventive method of processing mineral raw materials (containing precious metals and chlorides of alkali metals), including enrichment and roasting of the materials, the cider processing is carried out in two steps. At the first step, a secondary enrichment by means of water washing is carried out with a ratio of (S:L)=from 1:0.7 to 1:2.5, then the washed cinder is leached by hydrochloric acid with a ratio of (S:L)=from 1:2 to 1:3.

The distinctive features which make the proposed method different from the method earlier described as “the closest” (described in RU2291907), are the following: the cinder processing is carried out in two steps; at the first step a secondary enrichment by means of water washing is carried out with the ratio (S:L)=from 1:0.7 to 1:2.5, then the washed cinder id leached by hydrochloric acid with the ratio (S:L)=from 1:2 to 1:3.

In preferred embodiments, the method is carried out in the following way.

After the roasting of granules they are unloaded from a furnace into a reservoir of water and the ratio (S:L) is changed from 1:0.7 to 1:2.5 depending on the chlorides content. Then the chlorides of alkali and earth metals are dissolved, after which the washed cider is leached by hydrochloric acid with the ratio (S:L) from 1:2 to 1:3, and then the precious metals are recovered from the produced pulp by sorption.

Example 1.

A batch of insoluble residue was divided into 5 parts, which were washed off to remove chlorides up to various ratios. Then each sample of insoluble residue was separated from excessive solution, roasted and then precious metals were recovered from the produced ciders (see TABLE 1 below).

TABLE 1 Leaching of ciders by mixture HCl + HNO₃ Lump size of the cider: 2 mm Leaching parameters: ratio (S:L) = 1:4 Temperature: 90° C. Time: 4 hours Recovered, gram/ton from insoluble residue Cl content, % Pd Pt Au Ag 11.8 1.71 0.17 0.06 0.72 14.1 1.8 0.23 0.04 0.73 15.1 2.3 0.13 0.29 11.3 15.4 4.66 0.73 0.10 1.62 16.2 4.89 0.76 0.27 3.84

TABLE 1 shows that the excessive washing off to remove insoluble residue (decreasing of its C1 content) is followed by a considerable decrease of palladium content in the obtained product and therefore by a decrease of recovery of palladium.

Example 2.

Insoluble residue was roasted, and, after cooling and mincing thereof, the residue was leached by a 10% solution of aqua-regia with a ratio (S:L) =1:4. Pulp was produced with a KCl content of 43.6 g/dm³, a NaC1 content of 19.8 g/dm³, and a Pd content of 1.05 g/dm³ in the solution.

Example 3.

Two samples of insoluble residue were roasted under the same conditions as in the Example 2. The ciders were washed off to remove chlorides by means of water with the ratio (S:L) =1:2, and with the ratio (S:L) =1:3. The results achieved are shown in TABLE 2 below.

TABLE 2 Content of substances in the washing solution: Content in solution, of: Ratio Pd KCl NaCl (S:L) g/dm³ g/dm³ g/dm³ 1:3 not 57.9 25.3 detected 1:2 not 84.0 37.1 detected

The TABLE 2 shows that palladium doesn't transfer into the solution during the washing because its chloride decomposes when palladium is transferring in a water-soluble form due to the high temperature of roasting. The cider mass decreases by 24-25% after washing, the palladium concentration in the samples increases approximately 1.3 times.

After the leaching of the washed cider with the ratio (S:L) =1:2, the solution contains 3.0 gram/dm³ of KC1, 1.8 gram/dm³ of NaC1, and the palladium content increases up to 2.7 gram/dm³.

The enhanced technological effectiveness of the proposed method of processing mineral raw materials containing chlorides of alkali and earth metals derives from the fact that due to decreasing the volume of pulps produced during the leaching and therefore due to decreasing the amount of hydraulic-metallurgical equipment for the pulps' processing. The inventive method also allows for a significant increase of the output percentage of recovered precious metals. 

1. Method of processing mineral raw materials containing precious metals and chlorides of earth metals; the method consists of enrichment and roasting, with the following distinctive features: the cinder processing is carried out in two steps; at the first step a secondary enrichment by water washing is carried out with the ratio (S:L) =1:0.7-2.5, then the washed cinder is leached by hydrochloric acid with the ratio (S:L) =1:2-3. 